Combine several 'env DEBIAN_FRONTEND=noninteractive' instructions into one.

[hongyi-zhao]

I noticed that you used several times for the instrction 'env DEBIAN_FRONTEND=noninteractive' in your Dockerfile. I wonder why don't you only apply once of this command at the very beginning of the Dockerfile.

[mviereck]

It is possible to set this once at the beginning with

ENV DEBIAN_FRONTEND=noninteractive

This has the drawback that the variable is finally set in container, too. There it can cause issues using interactive terminal commands that behave different if DEBIAN_FRONTEND is set. For example, an application might skip [Yes|no] questions.

So I decided to use instead:

'env DEBIAN_FRONTEND=noninteractive apt-get [...]'

This way the variable is set for this one command only.

[hongyi-zhao]

If so, why not use it as following in the Dockerfile:

# set DEBIAN_FRONTEND
ENV DEBIAN_FRONTEND=noninteractive

# ... do stuff that needs the DEBIAN_FRONTEND during the build with apt-get.

# unset DEBIAN_FRONTEND
ENV DEBIAN_FRONTEND ""
#or
#ENV DEBIAN_FRONTEND ''
#or
#ENV DEBIAN_FRONTEND= 

[mviereck]

# unset DEBIAN_FRONTEND
ENV DEBIAN_FRONTEND ""

This does not unset the variable but sets it to an empty string. The variable itself remains. docker would need an UNSET instruction to really unset a variable. I am not sure if or how behaviour for set but empty DEBIAN_FRONTEND is defined. Setting it only where needed is the cleanest way for sure.

[hongyi-zhao]

docker would need an UNSET instruction to really unset a variable.

Do you mean I should write the instruction as shown below:

UNSET ENV DEBIAN_FRONTEND

I tried the above form and docker build will throw out the following error and terminate:

$ docker build --network host -f Dockerfiles/lion . -t deepin/lion
Sending build context to Docker daemon  35.84kB
Error response from daemon: Dockerfile parse error line 82: unknown instruction: UNSET

[mviereck]

docker does not have an UNSET instruction. That is why I set the variable for each command where it is needed.